It is known to convert video signals from interlaced format to non interlaced format in order to improve the apparent quality of reproduced images. In this procedure, in each field of video signal, lines of video signal are artificially generated, to occur interstitial to the standard field lines. Typical methods for artificially generating the interstitial lines include: repeating the values of the real line occurring immediately before or after the interstitial line; averaging the real lines occurring spatially above and below the interstitial line; averaging the real lines occurring temporally before and after the interstitial line; or a combination of the latter two methods. In the last mentioned method, spatially and temporally averaged lines are combined in proportions depending upon detected motion between image frames. A further method for generating interstitial lines, called fixed interpolation, includes averaging signals from a plurality of lines from a plurality of fields (e.g. five), which lines are symmetrically disposed about the interstitial line position.
Each of the foregoing systems have particular disadvantages. The repeat line systems generate jagged edges on diagonal lines. The spatial averaging system tends to exhibit a loss in vertical resolution. The temporal averaging system introduces motion artifacts. The motion adaptive system tends to be complicated and the performance of known motion detectors is marginal. For low amplitude video signals motion detectors tend to be unable to discriminate motion information from signal noise. Finally the fixed interpolator method is relatively expensive and does exhibit some motion artifacts.
It is an object of the present invention to provide a method and apparatus for generating interstitial video lines without undesirable artifacts using a minimum of processing circuitry.